1. Field of the Invention
The present invention relates generally to electronic devices designed for memory or data storage. It also is related generally to electronic devices designed for the switching and routing of electrical signals. The invention also relates generally to electronic devices whose critical dimensions are measured in nanometers, and, more particularly, to simple devices used as building blocks to form more complicated structures, and to the methods for forming such devices.
2. Field of the Invention
Random access memory (RAM) is becoming an increasingly important component of electronic hardware, with applications ranging from `smart credit cards` to computer storage, to name just two. Dynamic random access memory (DRAM) is based on silicon fabrication technology, and is a volatile memory characterized by a destructive read. This means that it is necessary to supply voltage to the memory bits at all times, or the information will disappear, Furthermore, each memory element has associated with it a transistor. This means that such memory devices will never be manufactured at a density that is greater than that allowable by the current generation of lithographic technology. Finally, reading the state of a DRAM bit will destroy the information in that bit.
More recently, a device called ferromagnetic RAM, or Fe-RAM, has been developed by a number of companies. A Fe-RAM device is a non-volatile memory bit which may be incorporated into something known as a cross-point memory array (see U.S. Pat. No. 5,640,343). The advantage of such an array is that the individual Fe-RAM devices do not require a transistor for every memory bit, but instead require on the order of n.sup.1/2 transistors for n memory bits. Fe-RAM is, however, characterized by a destructive read, similar to DRAM. Fe-RAM devices are based on the principle of using an electric field to change the magnetic moment of a ferromagnet. For certain materials, when this magnetic moment is changed, there is also a small change in the electrical resistance of the ferromagnetic material. For very small domains, this switching behavior no longer works, as ferromagnetic materials do not retain their ferromagnetic character when the size of the material becomes very small (i.e., less than 30 nanometers). Finally, the difference between a `1` and a `0` state in a Fe-RAM memory element is about a 15% change in resistance. This means that only relatively small cross-point memory arrays (less than 1 megabyte) of Fe-RAM can be constructed. It also means that FeRAM devices can only function as memory bits. They cannot function as true switches.
There recently has been developed electronic devices which are made up of two crossed wires between which is sandwiched an electrically addressable molecular species. These devices are simple and inexpensive to make. The devices can also be made to be extremely small with dimensions on the order of several microns down to a few nanometers. These devices can be used to produce crossbar switch arrays, logic devices, memory devices and communication and signal routing devices. Crossed wire or crossbar devices are disclosed in the following published patent applications:
U.S. patent application Ser. No. 09/292,767 entitled "Chemically Synthesized and Assembled Electronic Devices" [PD-10981971-1]; PA1 U.S. patent application Ser. No. 09/280,225 entitled "Molecular Wire Crossbar Interconnects for Signal Routing and Communications" [PD-10981966-1]; PA1 U.S. patent application Ser. No. 09/282,045 entitled "Molecular Wire Crossbar Logic" [PD-10981969-1]; PA1 U.S. patent application Ser. No. 09/282049 entitled "Demultiplexer for a Molecular Wire Crossbar Network" [PD-10981970-1]; and